The long-term objective of this application is an understanding of the mechanism of action of tumor necrosis factor (TNF). This cytokine is a mediator of inflammation that has pleiotropic effects on a variety of different cells. Three major lines of research are proposed: Identification of TNF-induced proteins and study of their biological role. TNF induces in human fibroblasts an inhibitor of plasminogen activator (PAI-2) that was identified by sequencing a cDNA from a library of TNF- treated cells. PAI-2 is not secreted by fibroblasts and its biological role as a cytoplasmic protein is unknown. Experiments are proposed to test whether PAI-2 protects human cells from TNF cytotoxicity. Two cDNA clones coding for unidentified proteins have also been cloned from the same library and will be fully characterized. Stimulation of the synthesis of secondary mediators. TNF induces synthesis of platelet-activating factor (PAF), but serum antiproteinases block this induction. Experiments are proposed to test whether PAF is produced only in zones of close adherence between cells, where the antiproteinases are excluded. Other experiments will investigate the mechanism of action of antiinflammatory peptides (antiflammins) that inhibit PAF synthesis. Inhibition of complement cytolysis inhibitor (CLI) by TNF. The mRNA for CLI has been detected in human fibroblasts and in some cancer cells. TNF suppresses expression of CLI mRNA. The experiments proposed will establish whether TNF regulates CLI synthesis at the transcriptional level. The presence of CLI mRNA in cancer cells may be relevant for the resistance of such cells to complement-mediated host defense mechanisms.